Limited by the instrument structure of volumetric illumination, samples outside the focal plane of wide-field fluorescence imaging can be excited and generate fluorescent signals, forming a significant defocus background that seriously interference the image data analysis. To suppress the defocus signal in a single wide-field image, we propose an image restoration algorithm based on three-dimensional (3D) point spread function (PSF) estimation and deconvolution, which efficiently removes the defocus signal. Through the reconstruction of simulated multi-layer circular rings and 3D experimental imaging of cellular actin, we verify the superiority of the proposed method in enhancing image details and improving resolution, providing an effective solution for high-quality fluorescence imaging under a wide-field microscope.